1. Field of the Invention
The present invention relates to a fluid powered positioning system having easy selectability of the order and locations to which a moving assembly can be automatically positioned.
2. Description of the Prior Art
In the past, automated manufacturing processes have principally been limited to large scale operations in which many thousands or even millions of like items are being fabricated. When such high quantity production is involved, considerable expense can be justified in providing customized automated manufacturing equipment. In the past, however, such automated equipment has by and large been unavailable to smaller scale manufacturing operations. The cost of purchasing automated positioning and parts handling equipment for limited production runs often far exceeds the saving that can be obtained by carrying out the manufacturing operations by machine rather than by human labor.
Thus a need exists for general purpose automation equipment that is low in cost and is sufficiently flexible so as to permit its use economically during low quantity production runs. One general class of equipment that is usable for many manufacturing processes is automatic positioning systems or robots, and a principal object of the present invention is to provide such a system which is sufficiently flexible and low in cost to permit its use in low volume manufacturing applications.
There are many manufacturing processes which require that a certain operation be performed at multiple different locations on a component. For example, a particular part may require several welds to be performed at fixed locations. If the quantity of parts being manufactured is great enough to justify the cost, this welding operation could be achieved by designing a special welding machine with five separate welding heads positioned at the desired locations. Such special tooling is out of the question for small scale operations. However, a similar result can be achieved by mounting the part on an automated positioning table that is controlled sequentially to move the part to the five requisite locations at each of which a conventional welding machine is used to perform individual welds.
Similarly, many manufacturing operations require the insertion of components at particular locations. For example, in electronic equipment, plural components may have to be inserted at corresponding locations on an interconnection board. The use of a positioning table that can move a component such as an electrical interconnection board sequentially to arbitrarily selected locations may enable the operation to be done with a simple component insertion machine, without the necessity for expensive custom equipment.
But although there has been a need for low cost, accurate positioning systems, this need has not been satisfied in the past. One limitation involves the number of available locations or stops to which the table can be moved. Complete flexibility of positioning can be achieved using a stepping or servo motor and calibrated lead screw to position a table along each axis. However, positioning systems utilizing such lead screw drives must have relatively complex electronic systems to accomplish the positioning operation. Such equipment can be programmed to move the table to any desired position, in any desired order, but the cost is high. Even if a smaller manufacturer could afford the capital investment, its use for low quantity runs has another shortcoming. That is, the reprogramming of the system is quite complex. Special training may be required to learn how to enter the requisite commands to step a new part in the correct order to a new set of locations.
If less flexibility is required with respect to the number of locations or their specific position, some low cost systems are available. For example, multi-position linear cylinder actuators are available commercially. In these, a hydraulic or pneumatically actuated cylinder assembly has a piston which can be positioned to two or more discrete locations when the fluid is applied to a corresponding one of a plurality of input ports. Such multi-position cylinders can be used in low cost positioning systems. However, they totally lack flexibility with respect to changing the locations to which the table or other moving assembly can be positioned.
Other low cost positioning systems have used multiple fluid cylinders, each having a different stroke distance, to obtain a certain degree of positioning flexibility. For example, such an automatic pneumatic control system is described in the article entitled "Piggy-back Cylinders Shuttle Work Piece" in Design News, Apr. 17, 1972. In the X-direction four cylinders, two 1/2-, a 1- and 1/4-inch stroke, are mounted in tandem. In the Y-direction, a 3/8- and a 13/16-inch stroke cylinder are mounted in tandem. By controlling the application and release of the cylinders, a selected pattern for movement of the workpiece-supporting table can be achieved.
In another known system, four linear cylinder actuators are used. A first pair is attached to the opposite ends of a first rack gear, and a second set, having a different stroke length from the first, is attached to opposite ends of a second rack gear. The two racks engage the same pinion to rotate the output shaft. By selectively pressurizing individual ones or pairs of the cylinders, five discrete angular output positions of the driven shaft can be achieved.
A distinct shortcoming of such prior art fluid cylinder actuator systems is that the number of different positions that can be achieved is very limited, the specific locations being limited to values set by the cylinder stroke.
Some effort has been made to overcome this limitation. Another known system used pneumatic or hydraulic cylinders to drive a movable table along a pair of slides until the table abuts against an adjustable travel stop or stops mounted on a drum or disc-like member. This type of "bang-bang" system is extremely limited with respect to the number of positions that can be obtained, and with respect to the mass and speed of moving parts. Although some flexibility is available with respect to adjustment of those few positions, the positioning device must return to a home position between moves from one stop position to the next one. In all of the above described systems, the positional feedback is always an "add on" feature, and the required load deceleration mechanism is complex and limits the speed of the slide.
Thus the need exists for a positioning system having the following features:
(a) relatively low cost; PA1 (b) multiple stop locations; PA1 (c) independently adjustable stop locations; PA1 (d) adjustment of the stop locations being simple, and not necessitating complex programming operations; PA1 (e) the order of stops being completely arbitrary and easily selectable; PA1 (f) no requirement that the positioning device return to a "home" position between moves from one stop location to the next; PA1 (g) the ability in a multiaxis embodiment, to move in any order in any axis, so that the positioned article can be moved around an obstacle; PA1 (h) programmable without complex digital equipment; PA1 (i) reasonably low in cost to enable its use in job shop and other low quantity manufacturing operations. PA1 (j) have a simple means of deceleration of moving parts; PA1 (k) have built in integral feedback; and PA1 (l) have intrinsical accuracy.
An objective of the present invention is to provide a fluid powered positioning system having all of these benefits.